1. Field of the Invention
The present invention relates to a driving method for a plasma display panel (hereinafter a PDP) and to a plasma display (PDP display). More particularly, this invention is concerned with a PDP driving method for improving display quality and a PDP display permitting improved display quality.
2. Description of the Related Art
In recent years, there have been great demands for diversified information to be displayed, for varied conditions for installation, for larger screen sizes, and for higher definition in the field of displays. The advent of a display meeting these demands has been awaited. Displays currently used in practice include various types of displays; a CRT, LCD, EL, fluorescent character display, light-emitting diode, and the like. PDP displays are drawing attention because of their excellent properties; no flicker, ease in making the screen larger, high luminance, long service life, and the like.
In the displays, needless to say, it is required to improve the display quality. Even in the PDP display, a further improvement in display quality is demanded.
PDP are available as a dual-electrode type in which two kinds of electrodes are used for selective discharge (addressing discharge) and sustaining discharge, and as a triple-electrode type in which the third electrode is used for addressing discharge. In a color PDP capable of gradational display, phosphors formed in discharge cells are excited by ultraviolet rays stemming from an electrical discharge. The phosphor has a drawback in that it is susceptible to the impact of ions that are positive charges stemming from a discharge. Since the dual-electrode type adopts the structure in which the phosphors are hit directly by ions, the ions may decrease the service life of each phosphor. To avoid this, the color PDP usually adopts the triple-electrode structure using surface discharge. Furthermore, the triple-electrode type is sub-divided into a type in which the third electrode is formed on a substrate on which the first and second electrodes responsible for sustaining discharge are arranged, and a type in which the third electrode is mounted on another substrate opposed to the substrate on which the first and second electrodes are arranged. Moreover, visible light emanating from a phosphor may be seen to be transmitted by the phosphor (transparent type) or to be reflected from the phosphor (reflective type). Moreover, the spatial coupling of each cell to be discharged to adjoining cells is disconnected by means of ribs or barriers. The ribs or barriers may be placed in four positions so that a discharge cell can be surrounded by ribs or barriers. Alternatively, the rib or barrier may be placed only on one side of a cell, and the coupling of the cell on the other sides are disconnected by optimizing the gaps (distances) between electrodes.
The present invention can apply to a plasma display panel (PDP) of any of the foregoing types, and relates to a driving method for any type of PDP and to a plasma display having the PDP. The present invention can thus apply to any kind of configuration. Herein, a description will be made by taking as an example a reflective type panel in which the third electrode is formed on another substrate opposed to a substrate containing electrodes responsible for sustaining discharge, in which a rib or barrier is formed only in a vertical direction (that is, ribs or barriers are orthogonal to the first electrode and second electrode and parallel to the third electrode), and in which part of each sustaining electrode is formed with a transparent electrode.
Gray-scale display in a plasma display is such that: one display frame is divided into a plurality of subframes having different lengths; bits of display data are associated with the subframes; and the lengths of the subframes are changed according to weights applied to the associated bits. One subframe is divided into a reset period, addressing period, and sustaining discharge period. During the reset period, a full-screen writing pulse is applied. All cells constituting all display lines are discharged irrespective of the preceding states of display. This is self-erasure discharge. The self-erasure discharge brings all the cells in a panel to a uniform state devoid of a wall charge. The reset period brings all the cells to the same state irrespective of the lit or unlit states of the cells during the previous subframe. The reset period is used to achieve the following addressing (writing) discharge on a stable basis.
During the addressing period, addressing discharge is carried out line-sequentially in order to turn on or off the cells according to display data. A scanning pulse is applied to a Y electrode. An addressing pulse is applied selectively to address electrodes of all address electrodes which coincide with cells to be lit. Consequently, discharge occurs between the address electrodes and Y electrode which specify the cells to be lit. With this discharge as a primer, discharge occurs between an X electrode and the Y electrode. Wall charges each having a magnitude permitting sustaining discharge are then accumulated on the surface over the X and Y electrodes. The same operation is performed sequentially on the other display lines. New display data is thus written on all the display lines.
Thereafter, during the sustaining discharge period, a sustaining pulse is applied alternately to the Y electrodes and X electrode. Sustaining discharge is then carried out. An image for one subframe is thus displayed. In this "addressing/sustaining discharge separated writing addressing method," a luminance is determined by the length of the sustaining discharge period; that is, the number of sustaining pulses.
In a driving method for a plasma display, addressing discharge, which is discharge to be performed according to display data, is carried out. A necessary and sufficient addressing discharge time (pulse duration of a scanning pulse) is varied depending on the lit or unlit conditions of cells that are located adjacently and that have been subjected to addressing discharge previously.
This is because when discharge has been performed at adjacent locations previously, intended addressing discharge is achieved rapidly and reliably. This is referred to as a priming effect. For example, when a scan is carried out line-sequentially from the top (first scan line) of a panel to the bottom (m-th scan line) thereof, a necessary and sufficient addressing discharge time for the n-th scan line depends greatly on the selected or unselected states of cells connected to the n-1-th or n-2-th scan line. In other words, when the priming effect is exerted because addressing discharge is performed on a preceding scan line or a scan line preceding the preceding scan line, a short pulse duration will do. However, when the priming effect is not exerted, a long pulse duration is needed. When the pulse duration of a scanning pulse does not meet a necessary and sufficient pulse duration, the probability of imperfect addressing discharge gets higher. In practice, cells that must be lit flicker or do not light. This leads to a marked deterioration in display quality.
In order to prevent the foregoing problem, the pulse duration of a scanning pulse should be made longer. However, the time allotted to addressing discharge is limited in terms of display speed. This measure cannot therefore be adopted it is possible that cells that must be lit flicker or do not light. This poses a problem in display quality.